Brad Pitt and Angelina Jolie

Though he was married to Jennifer Aniston at the time, Pitt couldn't take his eyes off of Jolie on the set of Mr. & Mrs. Smith in 2004. "I think we were the last two people who were looking for a relationship," Jolie later told Vogue. It wasn't until shooting nearly ended that Pitt and Jolie realized "it might mean something more than we'd earlier allowed ourselves to believe."